1. Field of the Invention
The present invention relates generally to the wide angle lens systems and more particularly to a retrofocus wide angle lens system having low distortion and highly corrected aberrations that is useful as a camera objective lens.
2. Description of the Prior Art
A demand has existed in the optical field for wide angle lens systems having a relatively high aperture ratio. In the field of photography, there is presently a demand to provide a wide angle photographic objective lens system that is capable of providing images having relatively low distortion. In compact single lens reflex cameras incorporating a reflecting mirror or prism, it is necessary that the back focal length be greater than the entire focal length of the lens system. It is known in the prior art to utilize retrofocus wide angle lens systems with single lens reflex cameras, for example, in the Shimizu U.S. Pat. No. 3,874,770. Problems however, have frequently occurred in correcting the aberration over a wide angle and in maintaining sufficient brightness for the desired photographic purposes.
Further examples of wide angle photographic lens systems can be found in the Mori U.S. Pat. No. 3,549,241 and U.S. Pat. No. 3,663,095, Shimizu U.S. Pat. No. 3,622,227 and U.S. Pat. No. 3,736,049, Takahashi et al. U.S. Pat. No. 3,870,402, Yamashita et al. U.S. Pat. No. 3,870,400 and U.S. Pat. No. 3,877,795 and Glatzel U.S. Pat. No. 3,864,026.
Recently, a Japanese patent application no. 44,326/1972 filed on May 4, 1972 in Japan was open to public inspection as No. 5,621/1974 on Jan. 18, 1974. The disclosed lens system was a retrofocus type wide angle lens system which included a first positive meniscus lens with its convex surface towards the object side; a second negative meniscus lens with its convex surface towards the object side; a third negative meniscus lens with its convex surface towards the object side and a fourth positive lens having an object surface radius of curvature of smaller absolute value than the image surface radius of curvature.